Signaling by electromagnetic waves.



No. 727,330. PATENTED MAY 5, 1903. R. A. FESSENDEN.

SIGNALING BY ELECTROMAGNETIC WAVES.

APPLICATION FILED IAB. 21, 1903.

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No. 727,330- PATENTED MAY 5, 1903..

R. A. FESSENDEN. SIGNALING BY ELECTROMAGNETIC WAVES.

APPLIOATIOI FILED [AB- 21, 1903.

I0 IODEL. 2 SHEETS-SHEET 2 NM wi w UNITED STATES Patented ma 5, 1903.

PATENT OFFICE.

SIGNALING BY ELECTROMAGNETIC WAVES.

SPECIFICATION forming part of Letters Patent N 0. 727,330, dated May 5,1903.

Application filed March 21, 1903. Serial No. 148,858- No model-l To allwhom it may concern:

Be it known that I, REGINALD A. FESSEN- DEN, a citizen of the UnitedStates, residing at Fort Monroe, in the county of Elizabeth City andStateof Virginia, have invented or discovered certain new and usefulImprovements in Signaling by Electromagnetic Waves, of whichimprovements the following is a specification.

The invention described herein relates to certain improvements inmethods of signaling by electromagnetic waves described in LettersPatent No. 706,742,'granted to me August 12, 1902, and has for itsobject a selective method of signaling which consists in varying thecharacter of the radiationsfrom the sendingestatiou at a rateindependent of the natural periodicities ofthe system.

The invention is hereinafter more fully described and claimed.

' .In the accompanying drawings, forming a partof this specification,Figure 1 is a diagrammatic view illustrating the apparatus employed atthe sending-station. Fig. 2 illustrates a modification of the sendingapparatus. Fig. 3 is a diagrammatic viewillustrating a form of receivingapparatus. Fig. 4. illustrates a form of receiver. Fig. 5 illustrates'asecond form of the receiver. Fig. 6 illustrates a modification of thereceiver shown in Fig. 5, and Fig. 7 is an end view of the receivershown in Figs. 5 and 6.

In thepractice of myinvention the primary 2 of a transformer is arrangedin series with the vertical conductor 1, which is grounded, as shown.The secondary 3 of the transformer is included in aoircuit consisting ofthe condensers 4 and 5 and a gap 6, which is normally non-eonducting-as,for example, an air-gap, a WVenhelt interrupter, or similar device. Thelocal circuit, including the secondary of the transformer, thecondensers, and the non-conducting gap, is preferably tuned to theperiodicity of the sending-conductor l. continuous-current kind andpreferably a storage battery, is arranged in series with the I condenserand secondary of the transformer,

and means, such as resistances 7 and 8, are included in the circuit ofthe generator, preferably, but not necessarily, in opposite legs of thecircuit. The generator'maybe ar- A generator 9, preferably of the tureof the gap. Very high voltages may be suitably obtained, if desired, busing a continuous-current generator with revolvingfield and making thesections of the winding of the armature primaries of transformers whosesecondaries are connected to a commutator and commutated by revolvingbrushes. In this way any desired amount of insulation can be obtained,and there is no need for heavy insulation on thegenerator itself, butmerely on the transformers and the commutator where there isno-diificulty in using it. The means 7 and 8 govern the rate at whichthe condensers Land fir'are charged, this function being described inUnited States Patent No. 706,742,. above referred to.

A motor 10, carrying its armature-shaft a commutator and regttlated asto speed by the tuning-fork 13 in; thef circuit' of the battery 12, asdescribedjin United States Patent No. 715,203, grantedvDecember 2, 1902,is employed for short-circuiting the retarding means orresistanc'efi,thereby varying the n umber of disohargespei' second atevery revolution of' the a'rmatureof the motor. A second tuning-fork l3and local battery 12* may be employed for regulating the motor, thoughthe same local battery may be used for both forks. When using'the'secondtuning-fork and battery, they are adapted to be connected to the motorby means of a switch 14. These tuning-forks have difierent rates ofvibration, and hence when one or the other is connected to the motor thelatter will rotate at different rates per second, causing acorresponding change in the number of times per secondthat the dischargefrequency is changed. As, for example, the circuits may be so arrangedthat the local circuit, including the secondary of the transformer, thecondensers, and gap,

has a natural period of two million per second, and the retarding means,as 7 and 8, may be so arranged that there will be two thousanddischarges per second'whenthe resistance 8 is in circuit and tenthousand discharges per second whenit is short-circuited. Then thecommutator .11, governed by the tuning-fork 13 or 13, may be so arrangedas to effect a change in the rate of discharge (and hence a change inthe amount of energy radiated) five hundred times per second. It willthus be seen that we have three different frequencies -first, theelectricahwave frequency,

ferred to tune the receiving-station electrically to the wave frequencyand to tune the receiver-mechanical] y or electrically, or both, to theindependent frequency. In the case illustrated the receivingcircuitwould be tuned electrically to'the wave frequency of two million and thereceiver tuned mechanically or electrically, or both, to a frequency offive hundred.

The distinct feature of this method is that there is not only electricaltuning, to the Wave frequency, but also tuning either mechanic- ,ally orelectrically, or both, to another frequency which is independent of thedischarge or group frequency.

It is'notessential that the resistance 8 be employed, as it may beomitted, in which case the commutator 1'1 entirely interrupts thedischarges the required number of times per second instead of varyingthe rate of discharge. ln sending messagesa key is used, which on beingdepressed short-circuits the retarding means or resistance 8 (or, ifthis is omitted, closes the discharge-circuit) during the time thesignal is being sent. The key 15 may also be arranged to operate in thisre verse way-i. e., to interrupt the discharges on being depressed.

The method described herein has the advantage over that described inLetters Patent No. 706,742 in that instead of employing acontinuous-current generator an alternatingcurrent generator having afrequency of from ten thousand to one hundred thousand per second, asdescribed in Letters Patent No. 706,737, granted to the August 12, 1902,may be used, inwhich case the energy radiated may be practicallyconstant. Int-he method described in Letters Patent N 0. 706,742 acontinuous voltage is used, or, if an alternating generator of the usualfrequency is employed,

the lower tuning is made to the frequency of thealternatinggenerator;but when an independent frequency, as" described herein, is used inconnection with an alternating-current generator the radiation occurs atfixed intervals of time, though the amount of energy radiated duringeach commutation may be and with usual frequencies will be unequal, andhence sharp mechanical tuning canbe had.

A particular advantage in the method described herein lies in thefactthat a slight variation in the voltage or speed of the generator doesnot affect the low-frequency tuning or tunin g to the lower frequency,whichin this case is the independent frequency.

As shown in Fig. 1, a rotating commutator 1'1, with a sending-key, maybe employed to shunt any desired amount of the resistance. When it isdesired to send two or more messages simultaneously, the amount ofresistance 7 and of other resistances in the charging-circuit may bevaried in substantiallythe same mannenas shown in Fig. 10 of Patent No.706,742, above referred to. To thisend a suitable shunting device,as'the rotating commutator 11, with a sending-key, is so arranged as tobe capable of shunting any desired amount of resistance 7 or otherresistances if more than two messages are to be sent, and so impose anarbitrary frequency dilferent from that imposed by commutator 11 andresistance 8 or other commutators and resistances when two or moremessages are to be sent sim ultaneously to two or more stations tuned todifferent independent frequencies;

At the receiving-station the receiver proper, which may be of theconstantly-receptive or automatically self-restoring wave-responsivetype, may be arranged in series with the receiving-conductor; but itispreferred to arrange such receiver in the circuit of the secondary of atransformer having its primary arranged in series with the vertical. Inthe circuit of the secondary 21 of the transformer are includedcapacities 23 and 24, preferably unequal, so as to permit sharp tuning.The circuit consisting of the'secondary of the transformer and thecapacities is preferably tuned electrically to the wave frequency of thesending end, and the receiver 25- is preferably tuned mechanically orelectrically, or both, to the independent frequency. A suitable form ofreceiver is shown in Fig. 4 and consists of a thin silver ring pivotallymounted on two silver knife-edges 27 and 28 and resting on a knife-edgeof carbon 29 and included with a coil 30, which is in series with thevertical conductor. One of the silver knife-edges, as 27, a portion ofthe ring, and the'carbon knife-edge 29 are included in a local circuithaving a battery and an indicating mechanism, as a'telephone. Thisconstruction of receiver is fully shown and described in Letters PatentNo.'706,736, granted to me August 12, 1902. Such a ring constructed ofNo. 40 silver wire has anatural elastic period of vibratiou of aboutfifteen per second.

A second form of receiver isshown in Fig. 5 and consists of a smalltuning-fork 31, made of thin phosphor-bronze about fifteenonethousandths of an inch thickand l1aving,ar-

matures 32 secured to its extremities, preferably formed of layers ofNo. 40 soft-iron wire. Between the ends ofthe tuning-fork anelectromagnet is arranged consisting of pieces of thin sheet-iron woundwith a coil of wire whose terminals may be connected in series with thevertical or in series with the secondary of the transformer having itspm- .4 will depend upon the periodicity of the alterquite.

mary connected to the vertical. It is found in practice that it issometimes beneficial when this form of receiver is used that it shouldbe very nearly tuned electrically to the wave frequency of thesendingstation, but not On waves being received at the sending-stationthe electromagnet 33 is energized and attracts the prongs ofthetuning-fork without change of direction so long as the radiation isbeing sent. When the motor 10 alters in the manner described the amountof energy sent out, either by changing the number of sparks per secondor by entirely interrupting the discharges, the prongs resume theiroriginal position. Every time the independent frequency of thesending-station is made equal to the natural period of the tunin g-fork31 there will be constantly-increasing amplitude of vibration. Toproduce an indication, one of the prongs may be directly fastened to atelephone-diaphragm 34, as shown in Fig. 5, or a microphonic contact 35,a local battery 36, and an indicating mechanism 37, as a telephone, maybe used, as shown in Fig. 6. The circuit including the microphoniecontact and telephone may also be tuned electrically to the independentfrequency, and this maybe done also when there is no mechanical tuning.The method described herein has a numberof advantages over thatdescribed in Patent No. 706,737, above referred to.

First, in the operation of the method de scribed in the patent it isevident that the group frequency would depend upon the voltage of thegenerator if a dynamo were used, for the higher the voltage the greaterthe number of discharges per second, and that if an alternator is used,since its voltage is constantly varying, the group frequency nator,since the groups available for mechanical tuning would have the sameperiodicity as the alternator. Consequently sharpness of tuning willdepend upon the speed regulation of the generator in all cases where adynamo is used It is found in practice that mechanical tuning can becarried to an accuracy of at least one part in four hundred, and it hasbeen carried to a much greater extent, though in general such extremeaccuracy is not-necessary. On the other hand, it has been founddifficult to regulate the speed of a dynamo within one part in twenty ortwenty-five. By this is meant not the average speed, but the extremevalues of instantaneous speed upon which the tuning depends. In theInethod'herein described this dilficul'ty is' entirely overcome, andinstead of attempting the extremely-difficult problem of regulating adynamo (giving, for example, several kilowatts output) to a constantspeed of one-fourth of one per cent. the dynamo regulation becomes analmost negligible factor, and the only speed which must be regulated isthat of a small motor consuming a few watts of energy and capable,therefore, of

being governed accurately by a standard tuning-fork. The method ofmechanicaltuning is thus made practical for the use of a generator otherthan storage batteries, while before it was only with the greatestdiificulty that accurate mechanical tuning could be attained.

In the method described in United States Patent No. 706,737 the numberof discharges per second-is limited, because the discharge frequency isthe frequency to which the mechanical tuning is tuned. Consequentlysince it is difficult to tune to very high periodicities mechanically avery high number of discharges per second cannot be used. In the methoddescribed herein the number of discharges per second may be very high.For instance, if an ordinary air-gap with air or magnetic blast be usedwe may obtain fifty thousand or more sparks per second. jbince, however,the independent frequency is independent of the discharge frequencies,we can thus combine the great radiating effect of high frequencies andyet obtain accurate me chanical tuning or accurate electrical tuning, orboth, to the lower frequency, in this case to the independent frequency.Being thus rendered independent of the frequency of the alternator wecan use a wide range of mechanical tuning with an ordinary alternator ofcommercial frequency. For example, if the periodicity of the alternatorbe sixty per second we can obtain mechanical tuning and of courseelectrical tuning over a range of frequency varying from ten per secondup to five thousand and higher from the same altern ator withoutchanging its periodicity. It is not essential that the tuning to theindependent frequency be mechanical or electrical alone, as both may becombined, though the use of either alone is preferred to the combinationof the two, and in many cases electrical tuning to both wave frequencyand electrical frequency maybe used.

In the extreme case, where the discharge frequency becomes identicalwith that of the wave frequency-as, for example, with a high frequencyalternating generator, as shown in Fig. 2the independent frequency maybe varied in the same way as inthe case described in Fig. 12'. 6., bymeans of the tuning-fork. It is preferred to have the commutator 11 witha number of segments, so as to change the discharge gradually andpreftoo IIO

erably to have the change vary as a sine.

trical circuitsas, for example, in the field of the dynamo of theauxiliary circuit 3 4 5 6 or in the vertical-with good results, but itis preferred to place it in the position shown.

When the commutator is placed in the vertical, it is preferred to usethe form of commutator construction described above, in which thealternation is effected gradually and not abruptly, as by aninterrupting form of commutator. This is on account of the fact that thevoltages used in wireless telegraphy are so high that if the circuit beinterrupted suddenly there vwill be difficulty from arcing between thecontacts of the interrupter.

It has been proposed to arrange a vibrating interrupter between thespark-gap and the vertical conductor; but such arrangement isinoperative, and its use has not, so far as known, been attempted.

On account of the high potentials necessary for wireless workit would bepractically Y impossible to operate such a vibrator so as to obtain asufiicient length of insulating-gap, especially with a vibrating form ofmake and break. In addition to the trouble from areing the interruptionswill be irregular, as the duration of the time of activityofthe verticalwill not depend solely on the period of the interrupter, but on thedistance the vibrating contacts happen to be separated and the sparkpotential at that time. For example, if the induction-coil primary isbroken at a time when the contacts are separated,

say, a distance of half an inch the spark will jump and the verticalwill be charged.

contacts have approached to within a quarter of an inch, the firstchange-spark will take place at a later point of time in the period ofthe vibration. Hence the times between successive charges and dischargeswill not be constant, and the tuning cannot be accurate- Thisd'ifiiculty'cannot be overcome by working in an insulating liquid, as,though the insulation is better before contact, an arc will be drawn inretracting, and it will be but a short time'before insulating power ofthe'liquid is destroyed.

I claim herein as my 'invention 1. In a system of signaling byelectromagwhich consists in varying the character of the radiationperiodically at a rate independent of'both the wave and dischargefrequencies.

3. In a system of signaling by electromagnetic waves, the method hereindescribed which consists in emitting waves of a given periodicity bydischarges of a given periodicity and periodically varying the characterof the radiation at a periodicity difierent from the naturalperiodicities of the system.

If however, theprimary is not broken until the 4. In a system ofsignaling by electromagnetic waves, the method herein described whichconsists in emitting waves of a given periodicity by discharges of agiven periodicity and periodically varying the character of theradiation at aperiodicitydiiferent from both the wave frequency and thedischarge frequency.

5. In a system of signaling by electromag'-- emitted energy and of theperiodicity of the generator.

8. In asystem of signaling the method herein described, which consistsin emitting energy periodically, periodically varying the character ofthe energy emitted at a periodicity independent of the periodicity ofthe emitted energy and of the periodicity of the generator, andoperating by the energy received at the receiving-station a receivertuned to the frequency of the emitted radiation and to the independentfrequency.

9. In a system of signaling the method herein described, which consistsin emitting energy periodically, periodically varying the character ofthe energy emitted-at a periodicity independent of the periodicity ofthe emitted energy and of the periodicity of the generator, andoperating by the energy received at the receiving-station a receivertuned electrically to the frequency of the emitted radiation andmechanically to the independent frequency.

10. In a system of signaling the method herein described, which consistsin emitting energy periodically, periodically varying the character ofthe energy emitted at a periodicity independent of the periodicity ofthe emitted energy and of the periodicity of the generator, andoperating by the energy received at the receiving-station a receivertuned electrically to the' frequency of the emitted energy, andoperating an indicating mechanism tuned to the independent frequency.

11. In a system of signaling by electromagnetic waves, the method hereindescribed which consists in generating electrical waves of a highfrequency,by means of electrical discharges ofa lower frequency, andperiodically changing the character of. the radiation at a rateindependent of the wave frequency and the discharge frequency.

IIO

12. In a system of signaling by electromagnetic waves, the method hereindescribed which consists in generating electrical waves of a highfrequency by means of electrical discharges, periodically changing thecharacter of the radiation at a rate independent of the wave frequencyand the discharge frequency, and operating by the energy so emitted 'areceiver at a receiving-station, tuned both to the Wave frequency and tothe independent frequency.

13. In a system of signaling-by electromagnetic waves, the method hereindescribed which consists in generating electrical waves of a highfrequency by means of electrical discharges, periodically changing thecharacter of the radiation at a rate independent of the wave frequencyand the discharge frequency, and operating by the energy so emitted areceiver, at a receiving-station, tuned electrically to the wavefrequency and mechanically to the independent frequency.

14. In a systemof signaling the method herein described, which consistsin emitting energy periodically from a sending-station and periodicallyvarying the character of the energy emitted at a periodicity independentof the periodicity of the emitted energy and of the generator, andproducing by the energy so emitted indications at a receiving-station bymeans of a cumulatively-acting receiver.

15. In a system of signaling by electromagnetic waves, the method hereindescribed which consists in generating electrical'waves of a highfrequency by means of electrical discharges, periodically changing thecharacter of the radiation at a rate independent icall y varying thecharacter of such radiation at a rate independent of the naturalperiodicities of the system and operating by the energy received at thereceiving-station a receiver of the character substantially as describedtuned to the frequency of the emitted radiation and to the independentfrequency.

17. In a system of signaling by electromagnetic waves, the method hereindescribed, which consists in the generation of radiation, varying thecharacter of the radiation periodically at a rate independent of bothwave and discharge frequencies and operating at the receiving-station areceiver of the character described tuned to the frequency of theemitted radiation and to the independent frequency.

18. In a system of signaling by electromagnetic waves the method hereindescribed, which consists in emitting waves of a given periodicity bydischarges of the given periodicity, periodically varying the characterof the radiation at a periodicity different from the naturalperiodicities of the system and operating by the energy received at thereceiving-station a receiver of the character described tuned to thefrequency of the emitted radiation and to the independent frequency.

19. In a system of signaling by electromagnetic waves, the method hereindescribed, which consists in emitting waves of a given periodicity bydischarges of a given periodicity, periodically varying the character ofthe radiation at a periodicity different from both the wave frequencyand the discharge frequency and operating a receiver of the characterdescribed tuned to the frequency of the emitted radiation and to theindependent frequency.

In testimony whereof I'have hereunto set my hand.

REGINALD A. FESSENDEN.

Witnesses:

T. L. SCLATER, O. S. MARIE.

